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Increase by Metyrapone Is Prevented by Dexamethasone Pretreatment

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Increase by Metyrapone Is Prevented by Dexamethasone Pretreatment Journul of' Neuroendocrinolo~~,Vol. 2, No. 6 @ 1990 Oxford University Press, 0953-8194/90 $3.00 Characterization of Glucocorticoid Binding Capacity in Human Mononuclear Lymphocytes: Increase by Metyrapone is Prevented by Dexamethasone Pretreatment Rainer Rupprecht, Johannes Kornhuber, Norbert Wodarz, Claudia Gobel, Johannes Lugauer, Christian Sinzger, Helmut Beckmann, Peter Riederer and Otto Albrecht Mullert Psychiatrische Klinik, University of Wurrburg, Wurzburg, FRG t Medizinische Klinik Innenstadt, Universlty of Munich, Munich, FRG Key words. glucocorticoid binding, metyrapone, dexamethasone, lymphocytes, man Abstract Autoregulation of receptor systems by their own ligands is a well established biological phenomenon. While down-regulation of the glucocorticoid binding capacity by glucocorticoids has been shown in animals and humans, data on up-regulation processes in humans are lacking. To further explore glucocorticoid receptor plasticity in relation to endogenous ligands, glucocorticoid binding parameters were assessed in 15 healthy controls before and after oral administration of 1.5 g metyrapone with and without dexamethasone pretreatment. Administration of metyrapone resulted in blockade of the feedback of the hypothalamic-pituitary- adrenal system as shown by the rise in adrenocorticotropin levels, while pretreatment with 1 mg dexamethasone completely suppressed adrenocorticotropin concentrations. Glucocorticoid binding sites per lymphocyte exhibited an increase of 63% following metyrapone administration, which was prevented by dexamethasone pretreatment. Comparison of morning and afternoon glucocort- icoid binding sites per cell in 11 healthy volunteers further revealed a diurnal rhythm of glucocorticoid receptor sites. These data suggest that human lymphocyte glucocorticoid receptors are under autoregulatory control. Glucocorticoid receptors (GR) have been identified in numerous achieved by metyrapone (MET) administration in healthy volun- mammalian and human tissues including brain (1 -3), liver (4), teers mimicking the effect of adrenalectomy and whether this can lung (51, skin (6, 7),and peripheral blood cells (8-10). Although be rcvcrsed by exogenous glucocorticoids. several lines of evidence suggest an immunosuppressive effect of glucocorticoids with therapeutic implications (1 I), the exact mcch- anism of glucocorticoid action in relation to immune function remains unsolved. Glucocorticoids have been shown both to Results inhibit lymphocyte proliferation (1 1) and to inducc redistribution of circulating lcukocytcs to thc bone marrow (1 I). Phurmucologicul churactrristics qf' the GR Exposure to higher doses of glucocorticoids can down-regulate Linear regression analysis was performed on all saturation experi- the GR in animals (12) and humans (13, 14). In addition, ments; a representative Scatchard plot is shown in Fig. 1, Satura- investigations on GR pharmacology in human leukocytes at tion experiments clearly revealed only one binding site. The Hill different times of day (10, 15, 16) or in adrenocortical disorders coefficient was close to unity (1 .OOfO.OOl), indicating an absence (10, 17, 18) have provided conflicting evidence for a diurnal of cooperativity of the binding site. rhythm of GR (15) and dccrcascd GR numbers in adrenal Specific binding of 6 nM [3H]dexamethasone (['HIDEX) was insufficiency (18) or Cushing's syndrome (19), which others were completely displaced by the pure glucocorticoid agonist RU 28362 unable to confirm (10, 17). with a Ki value of 7.8f2.1 nM, by DEX with a Ki value of Down-regulation of GR by glucocorticoids has been relatively 13.4 & 1.7 nM, and by cortisol with a K, value of 117 f 3 1 nM, easy to study in either experimental animals or man, while data respectively, under equilibrium conditions in three different on up-regulation phenomena are available only from animals experiments. after adrenalectomy (20). Thc present study was designed to There was a linear relationship between absolute CR and explore whether an increase in GR binding capacity can be lymphocyte number in the assay. ~ Correspondence 10: R. Rupprecht, Max-Planck-Institute of Psychiatry, Kraepelinstr. 2- 10, 8000 Munchen 40. FRG 804 Glucocorticoid binding capacity in human lymphocytes SCATCHARD PLOT GLUCOCORTICOID RECEPTOR SITES PER CELL B/F -3 6000 3 1 5000 4000 3000 \ \ 2000 1000 n- 0 / Baseline MET MET+DEX 0 5 10 15 20 Bound [M]-’*/lO ’ cells GLUCOCORTICOID RECEPTOR REGULATION FIG.1, Scatchard plot of a representative saturation experiment of specific FIG.3. Mean f SE plasma glucocorticoid receptor (GR) binding sites per [3H]dexamethasone binding to human mononuclear leukocytes. Specific- cell at 1600 h on three consecutive days in 15 healthy controls under ally bound/free [3H]dexamethasone is plotted versus specifically bound baseline, metyrapone (MET) and metyrapone plus dexamethasone [3H]dexamethasone. (MET + DEX) pretreated conditions. GR sites per cell are significantly increased by MET administration (t= 3.98, df= 14, P<O.OOI). This increase is prevented by DEX pretreatment. Glucocorticoid binding cupucity in relution to endogenous glucocorticoid levels in vivo KD (nM) Assessment of diurnal variation of GR binding pharmacology revealed a marked increase of GR sites per cell in the afternoon - (2542 f 504 versus 4060 f 1 184 receptor sites per cell; t = 4.33, 25 df= 10, P<O.OOl) contemporaneous with a pronounced fall in r plasma cortisol (557.3 & 141.5 versus 273.1 & 144.5 nmol/L; t= 5.55, df= 10, P<O.OOl), while the K, did not change significantly 2oj15 T (8.6f2.7 versus 10.3k3.3 nM). Administration of MET resulted in blockade of llB- 10 hydroxylase activity shown by the rise in adrenocorticotropin (ACTH) (Fig. 2; t = 4.5, df= 14, P < 0.001), which was prevented by DEX pretreatment. MET administration also increased the 5 GR sites per cell by 63% within 7 h (Fig. 3; t=3.98, df= 14, P<O.OOl), and this effect was blocked by low dose DEX pretreat- 0 ment. Depletion of endogenous glucocorticoids by MET and Baseline MET MET+DEX GLUCOCORTICOID RECEPTOR REGULATION ACTH (pmol/L) FIG.4. Meanf SE K, values at 1600 h on three consecutive days in 15 healthy controls under baseline, metyrapone (MET) and metyrapone plus 35 dexamethasone (MET + DEX) pretreated conditions. 30 subsequent replacement by DEX did not significantly alter the 25 K, (Fig. 4). 20 No relationship was found between age, sex, body weight, ACTH, or baseline cortisol levels (223.7k75.6 nmol/L) and GR 15 binding parameters under the conditions studied. 10 Discussion 5 Although previous investigations of a possible diurnal rhythm of 0 GR binding parameters have yielded contradictory results (10, Baseline MET MET*DEX 15, 16), the present study demonstrated clear diurnal rhythm of FIG.2. Mean SE plasma adrenocorticotropin (ACTH) concentrations GR sites with no apparent change in GR affinity. Interestingly, at 1600 h on three consecutive days in 15 healthy controls under baseline, we did not observe a significant correlation between GR sites metyrapone (MET) and metyrapone plus dexamethasone (MET + DEX) and ACTH or cortisol levels, suggesting that plasma concentra- pretreated conditions. ACTH levels are significantly increased by MET administration (t=4.5, df= 14, P <0.001). This increase is prevented by tions of endogenous glucocorticoids at the time of the GR assay DEX pretreatment. do not control the GR sites. Estimation of cortisol profiles several Glucocorticoid binding capacity in human lymphocytes 805 hours prior to that of GR sites however might clarify the France). Rotiszint 22 was obtained from Roth (Karlsruhe, West Ger- relationship of GR sites and endogenous glucocorticoids. many). The incubation buffer consisted of PBS with 5 mM D-glucose added. Stock solutions of unlabelled steroids (50 pM) were prepared in We demonstrated an increase in GR activity binding 7 h incubation buffer containing 5% ethanol. following MET pretreatment. At this time ACTH levels had also increased dramatically due to the lack of feedback action of 1113- Preparation of cells hydroxylated endogenous glucocorticoids. This increase could be A mononuclear cell fraction was prepared by sodium metrizoate-Ficoll prevented by prior administration of the synthetic glucocorticoid density gradient centrifugation (26). Cells were washed two times in PBS for 10 min, incubated for 60 min at 37 "C, and then washed again to DEX. Since glucocorticoids probably need several hours to exert allow dissociation of endogenous hormone. Endogenous cortisol levels a notable influence on GR regulation, this might explain the lack after the washing procedure were below the detection limit of the assay. of correlations between GR sites and plasma cortisol concentra- The final concentration of cells was determined using a Coulter Counter tions at the time of the GR assay. (Model S5; Coulter Electronics Ltd, England). Viability of cells exceeded 95%, as judged from their ability to exclude trypan blue. Contamination Our results in humans accord with those of animal studies and by erythrocytes was less than 10%. contamination by granulocytes and recent in vitro investigations at the protein and DNA level. A monocytes was less than 8% and did not differ between the three test rise in GR sites in the rat brain has been observed following days. adrenalectomy (20), while exposure to glucocorticoids results in Binding assay a down-regulation of GR sites of various cell lines (13, 14, 21). Binding experiments were carried out at 37 'C in plastic microtitre plates While glucocorticoids reduce
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